Multilink

Multilink (from scenerystack/axon) links a callback to multiple Properties at once, calling it whenever any of them change. It's the callback-only sibling of DerivedProperty: use it when you need a side effect (repositioning a Node, playing a sound, logging) rather than a new derived value.

import { Multilink, NumberProperty } from 'scenerystack/axon';

const xProperty = new NumberProperty( 0 );
const yProperty = new NumberProperty( 0 );

Multilink.multilink( [ xProperty, yProperty ], ( x, y ) => {
  console.log( `position: (${x}, ${y})` );
} ); // logs "position: (0, 0)" immediately

xProperty.value = 5; // logs "position: (5, 0)"

Static convenience methods (preferred)

The static factories are preferred over new Multilink(...) directly, both because they read better and because a bare new Multilink(...) with no captured reference trips lint rules for side-effect-only construction:

Method	Behavior
Multilink.multilink( dependencies, callback )	Links and calls callback immediately with current values
Multilink.lazyMultilink( dependencies, callback )	Links without an immediate callback
Multilink.multilinkAny( dependencies, callback )	Same as multilink, but for a dynamically-sized array of dependencies (callback takes no arguments)
Multilink.lazyMultilinkAny( dependencies, callback )	Lazy version of multilinkAny
Multilink.unmultilink( multilink )	Disposes a Multilink instance — equivalent to calling .dispose() on it

const multilinkHandle = Multilink.multilink(
  [ xProperty, yProperty ],
  ( x, y ) => console.log( x, y )
);

// later
Multilink.unmultilink( multilinkHandle );

Constructor

new Multilink( dependencies, callback, lazy? )

Up to 15 dependencies are supported via overloads (like DerivedProperty), with callback's parameter types inferred from the dependency array. Pass lazy: true as the third argument to suppress the initial callback.

Members

Member	Effect
dispose()	Unlinks the callback from every dependency. Calling dispose() twice throws an assertion error

Multilink vs. DerivedProperty

Reach for DerivedProperty when the combination of dependencies is a value other code should read and link to (e.g. an areaProperty other Nodes bind their size to). Reach for Multilink when you only need to run something when several Properties change together and there's no resulting value worth exposing as its own Property.